Conventionally, amorphous silicon powder and amorphous silicon coating film are prepared by thermal decomposition of SiH.sub.4, Si.sub.2 H.sub.6, Si.sub.3 H.sub.8, etc. However, these compounds are very unstable to oxygen, and susceptible to explosion, and thus must be handled in an inert atmosphere. These compounds must be stored in cylinders because of the high vapor pressure thereof, and are not easy to handle. Further, these materials are not necessarily inexpensive. Therefore, less reactive and more stable substances are wanted as materials for preparation of powder and coating film of amorphous silicon.
We have found that amorphous silicon can be prepared by thermal decomposition of chloropolysilanes, which are stable and free from danger of explosion.